Continue to conduct the study in accordance with the common protocol and manual of procedures developed by the Steering Committee and the Coordinating Center at the University of California at Los Angeles. During the period of this contract modification, it is expected that the Contractor will trace and obtain medical information on the next 2,000 medical source referrals on the randomized list provided by the Coordinating Center, and identify, trace, and obtain medical information on appropriate controls for these cases. In addition, data collection will be completed on any unfinished subjects from among the 2423 medical source referrals and their controls, undertaken in previous contract periods.